Percentage Calculator
A percentage calculator finds a part of a number, compares values, and works out increases, decreases, and reverse percentages. Choose one of seven modes to see the result, substituted formula, and steps as you type.
Result
Enter two numbers to see your result.
What is a percentage calculator?
A percentage calculator answers questions about parts, rates and relative change using values you enter. It can find a percentage of a number, express one value as a percentage of another, compare two values, apply an increase or decrease, or work backwards from a known percentage.
This calculator updates as you type, shows the selected formula and substitutes your numbers into the working. Inputs stay in the browser; displayed results can be rounded to between zero and six decimal places.
How to calculate percentages: seven formulas
What is X% of Y? Formula: (X / 100) × Y. Example: 15% of 200 = (15 / 100) × 200 = 30.
X is what percent of Y? Formula: (X / Y) × 100. Example: 30 is (30 / 120) × 100 = 25% of 120.
Percentage change from old to new: ((new − old) / |old|) × 100. Example: from 80 to 100, the absolute difference is 20 and (20 / |80|) × 100 = 25% increase.
Percentage difference between A and B: |A − B| / ((A + B) / 2) × 100. Example: for 50 and 70, 20 / 60 × 100 = 33.33% when rounded to two decimal places.
Increase Y by X%: Y × (1 + X / 100). Example: increasing 80 by 20% gives 80 × 1.2 = 96.
Decrease Y by X%: Y × (1 − X / 100). Example: decreasing 80 by 20% gives 80 × 0.8 = 64.
Reverse a percentage when Y is X% of an unknown number: Y / (X / 100). Example: if 30 is 20% of a number, 30 / 0.2 = 150.
Percentage change, percentage difference, and percentage points
Choose percentage change when a value moves from a known starting point; choose percentage difference when two values have equal standing. Percentage points measure the direct subtraction of two percentages, not their relative change.
| Measure | Formula | Use it when |
|---|---|---|
| Percentage change | ((new − old) / |old|) × 100 | There is a defined old value and direction matters. |
| Percentage difference | |A − B| / ((A + B) / 2) × 100 | Comparing two values without choosing a baseline. |
| Percentage points | New percentage − old percentage | Subtracting one rate from another. |
Common percentage calculator uses
Use percentage-of mode to work out a tip or sales tax amount, then increase the bill by that rate to estimate a total. Use decrease mode for a discount, or percentage change to compare sales, grades and growth rates over time. Increase mode can estimate a markup from cost; a profit margin instead divides profit by the selling price, so markup and margin are not interchangeable.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 15% of 200 is (15 / 100) × 200 = 30.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the absolute old value, then multiply by 100. A change from 80 to 100 is a 25% increase.
How do I calculate a discount?
Multiply the original price by 1 minus the discount rate divided by 100. A 20% discount on 80 leaves 80 × 0.8 = 64.
What is the difference between percentage change and percentage difference?
Percentage change compares a new value with a defined old baseline. Percentage difference compares two values using their average, without assigning either one as the baseline.
Can percentage change exceed 100%?
Yes. An increase can be more than 100% when the new value is more than twice the old value. A decrease from a positive old value cannot be below −100% if the new value is nonnegative.
Why is percentage change from zero undefined?
Percentage change divides by the absolute old value. When the old value is zero, that denominator is zero, so no finite percentage change is defined.
What is the difference between percent and percentage points?
Percent describes a relative rate. Percentage points are the arithmetic difference between two percentage rates; a change from 20% to 25% is 5 percentage points, or a 25% relative increase.
How do I reverse a percentage?
Divide the known amount by the percentage written as a decimal. If 30 is 20% of the original number, calculate 30 / 0.2 = 150.
Can I use negative or decimal values?
Yes. Enter negative values or decimals directly; commas and spaces are removed from pasted numbers.
Are my values uploaded or saved?
No. The calculator runs in your browser and does not send or save the values you enter.
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